Field of the Invention
This invention relates to apparatus for testing the alignment of the road wheels of vehicles. As applied to the front wheels of a motor vehicle, the parameters most usually required to be determined are those of toe-in or toe-out of the wheels, but in some cases it is also required to measure the camber angle of the axes about which the wheels swivel.
It is desirable when the alignment of vehicle wheels is to be tested that the required test should be carried out under conditions as close as possible to those pertaining when the vehicle is being driven, i.e. with the weight of the vehicle carried by the wheels and with the wheels rotating. To this end it has been proposed to position the vehicle so that the wheels under test rest on rotatably driven rollers, the required alignment parameters then being measured by suitable transducers which sense the positions of parts of the wheels or tyres.
A problem arises with apparatus of this type in that irregularities in the tyre or wheel rim can give rise to incorrect readings, particularly if the transducers are not correctly positioned relative to the axis of rotation of the wheel. Further, if parts of or associated with the transducers are required to contact the wheel, they must be constructed to withstand abrasion caused by such contact and despite this may be subject to rapid wear. It is also necessary accurately to set up the equipment to suit a particular vehicle having particular wheel dimensions, if consistent and accurate results are to be produced.